DESCRIPTION: (Adapted from the applicant,s abstract) This research project will develop a MAb based system to reversibly permeabilize the BBB to blood- borne therapeutics. Such antibodies also may serve as carrier molecules to bring therapeutics to the BBB. To this end, a naturally occurring receptor on brain endothelium that may be involved in leukocyte migration into the brain will be examined. The presently available MAbs cross react with cerebral capillaries from human, rat, and rabbit. Preliminary studies have shown that upon intravenous injection into rabbits the antibodiesinduce transient BBB permeability and block leukocyte migration into the CSF.They demonstrate the feasibility of this approach for delivery to the brain. Phase I research will focus on a MAb that recognizes rat and human cerebral capillaries. In rat, experiments will be designed to address the following: l) time and dose dependence of antibody localization to cerebral capillaries, 2) antibody- induced transient permeability ofthe BBB to blood-borne molecules, 3) specificity for the cerebral endothelium, 4) delivery of antibody-protein conjugates to the BBB, and 5) action of antibody fragments. Additionally, isolation of the rat cerebral capillary receptor polypeptide(s) will be initiated. Phase II work will concentrate on isolation of the human receptor and development of second generation antibodies that may show increased efficacy.